Stock lifters previously have been provided arranged in pairs and spaced from one another along a row of progressive dies with lifters of each pair located at opposite side edges of a strip of sheet stock material upon which die operations were performed. There have also been provided transverse grooves near the outer or free ends and in adjacent sides of the lifters of each pair into which grooves the opposite edge portions of the strip stock material have extended for slidably supporting and guiding the strip stock material as it has progressively advanced to and from the different dies. As shown in U.S. Pat. No. 2,979,004 to Kenville, et al., these grooves have been slightly curved and extended across about the half of the periphery of the lifter that faced inwardly toward the strip stock material, and such grooves have been beveled at their edges apparently to aid in the receipt and guiding of progressive strip stock material.
These lifters have had their inner or lower end portions slidably supported in the lower die members for limited longitudinal movement in a vertical direction whereat they have been engaged by the upper die members during downward movement of the upper die members and thereby have lowered the strip stock material onto the lower supporting die members for punching, forming or other desired die operations. Springs have been located in recesses in the lower die members under the lifters which have been compressed during the lowering of the upper die members and which have then urged the lifters outward and such strip stock material upward upon the return of the upper die members to their upward inactive positions. The raising of the strip stock material has disengaged the same from the lower die members and positioned same above the parts of the lower die members so as to provide clearance for advancement of the stock material along the row of progressive dies.
In order to control the extent of upward travel of the lifters and strip stock material and to retain the lifters in the lower supporting die member, hold-down fasteners in the form of screws or bolts with circular washers have been provided outboard in the lower supporting dies located immediately adjacent to the lifters and on the side of the lifters directly opposite from the side bearing the stock supporting and guide groove. The side of the lifter so opposite such groove has heretofore been machined with a longitudinal groove, arcuate in cross-section, and extending transversely about a quarter of the way through the lifter so as to receive a corresponding portion of the hold-down fastener washer. This longitudinal groove has extended from just below the head to a medial portion of the lifter of such distance to provide for desired lifter travel. At such medial termination point there has been provided a shoulder at the bottom of such longitudinal groove to be contacted by the hold-down fastener.
This prior stock lifter arrangement has suffered from a number of shortcomings, however. Firstly, having the lifter constructed so that the hold-down fastener is oriented directly opposite from the lifter's stock material supporting and guiding groove, has meant that such hold-down fastener has had to be positioned in the lower die directly outboard the stock material receiving area, thus requiring the lower dies to be of additional sufficient width to receive such hold-down fastener, a significant economic detriment considering the substantial thickness and size of such dies. Likewise, the involved nature of the particular construction of these prior lifters has made these lifters relatively difficult to form and therefore expensive, especially considering their requirements in multiple number in typical applications. Furthermore, by being mounted so fixedly against rotation, there has been a tendency of prior stock lifters to jam and impede the progress of less than perfectly positioned strip stock material. Such fixed position against rotation has also presented single contact and bearing surfaces during use resulting in extensive localized wear.